The study aimed to evaluate the safety and efficacy of simultaneous integrated dose reduction intensity-modulated radiotherapy (SIR-IMRT) in patients with locally advanced non-small-cell lung cancer (LA-NSCLC). In the SIR-IMRT conhort, the prescribed irradiation dose was 60 Gray (Gy) for the planning gross tumor volume (PGTV) and 54 Gy for the planning target volume (PTV), while in the conventional intensity-modulated radiotherapy (C-IMRT) cohort, it was 60 Gy for both PGTV and PTV. The SIR-IMRT group demonstrated better overall survival (OS) than the C-IMRT group, with a median OS of 37.7 versus 31.2 months. The SIR-IMRT group also experienced lower cardiac and esophagusal doses, along with a lower incidence of acute radiation esophagitis and ≥ grade 3 radiation pneumonitis. HeartV20 (the volume of the heart receiving at least 20 Gy) was the only independent risk factor associated with survival. SIR-IMRT significantly reduced cardiac irradiation exposure, improving patient survival and offering a new therapeutic direction for future studies.